SEBI's Closing Auction Session (CAS): Everything You Need to Know (Effective August 3, 2026)
The Indian stock market is set to witness an important change from August 3, 2026. As per SEBI and Exchange guidelines, the Closing Auction Session (CAS) will be implemented as a new mechanism for determining the official closing price for equity stocks that have active Futures & Options (F&O) contracts.
This initiative aims to improve price discovery, enhance market transparency, and ensure a fair and efficient closing price.
What is Changing from Aug 3, 2026
Currently, the official closing price is determined using the Volume Weighted Average Price (VWAP) of trades executed during the last 30 minutes of the regular trading session, i.e. from 3:00 PM to 3:30 PM on every trading day.
From August 3, 2026, this process changes.
The closing price will now be determined through a dedicated Closing Auction Session (CAS).
Instead of continuous trading determining the closing price, eligible buy and sell orders will be matched during an auction and a single equilibrium price, where the maximum quantity can be traded, will become the official closing price.
Additionally, Equity Derivatives market timings will be extended from 3:30 PM to 3:40 PM.
Why is CAS Being Introduced?
The Closing Auction Session aims to:
- Improve price discovery at market close.
- Reduce the impact of large trades on the closing price.
- Provide better benchmark prices for Mutual Funds, ETFs, and Index calculations.
- Facilitate efficient execution of large institutional orders.
- Align Indian markets with global exchange practices.
Applicability
The Closing Auction Session will be applicable only to Cash Market securities in which derivative contracts are available.
Cash Market securities that are not eligible for CAS will continue to trade under the existing market timings until 3:30 PM.
The Reference Price for CAS will be calculated based on the VWAP of trades executed between 3:00 PM and 3:15 PM.
CAS Timeline
(can make a 3 column table)
3:15 PM to 3:20 PM – Transition from CTS to CAS
During this time, the Reference Price is calculated.
No order placement or modification is permitted.
Pending Stop Loss Orders, Iceberg Orders, and orders outside the revised price band will be cancelled by the Exchange.
3:20 PM to 3:25 PM – Order Entry Period
You can place fresh Market Orders and Limit Orders.
Existing orders can also be modified or cancelled within the applicable ±3% price band.
3:25 PM to 3:25 PM – Random Close between 3:28 PM to 3:30 PM
Only Limit Orders can be placed, modified, or cancelled.
Market Orders cannot be modified or cancelled.
3:30 PM to 3:35 PM – Auction Matching
Auction matching takes place, trades are confirmed, and the equilibrium price becomes the official closing price.
Revised Auto Square-off Timings
Cash Market
- Pre Auto Square-off will move from 3:15 PM to 3:05 PM.
- Auto Square-off will move from 3:20 PM to 3:10 PM.
Equity Derivatives
There is no change.
- Pre Auto Square-off remains 3:15 PM.
- Auto Square-off remains 3:20 PM.
Important Points to Remember
- CAS is applicable only to eligible Cash Market securities having derivative contracts.
- Trading during CAS will be restricted to ±3% of the Reference Price.
- Stop Loss Orders and Iceberg Orders are not permitted during CAS.
- Unexecuted Limit Orders from CTS will be carried forward to CAS, except Stop Loss Orders, Iceberg Orders, and orders outside the applicable CAS price band.
- Securities not covered under CAS will continue normal trading till 3:30 PM.
Changes in Equity Derivatives
Equity Derivatives market timings will be extended until 3:40 PM.
This extension is applicable to both Stock Derivatives and Index Derivatives.
Additionally:
- The Reference Price for Stock Futures will be based on the VWAP of trades executed between 3:00 PM and 3:15 PM.
- From 3:15 PM to 3:40 PM, Stock Futures will trade within a ±3% price band based on the calculated Reference Price.
Current Closing Price Mechanism vs. Closing Auction Session (CAS)
| Current Process (Till August 2, 2026) | Closing Auction Session (From August 3, 2026) |
| Official closing price is determined using the Volume Weighted Average Price (VWAP) of trades executed between 3:00 PM and 3:30 PM.
|
Official closing price is determined through a dedicated Closing Auction Session (CAS), where eligible buy and sell orders are matched to arrive at a single equilibrium price. |
| Closing price is based on continuous trading. | Closing price is determined through an auction mechanism. |
| Regular Cash Market trading continues until 3:30 PM. | Eligible Cash Market securities participate in CAS, while securities not covered under CAS continue to trade under existing market timings until 3:30 PM. |
| Equity Derivatives market closes at 3:30 PM. | Equity Derivatives market timings are extended until 3:35 PM. |
Quick Timeline of the Closing Auction Session (CAS)
| Time | Activity |
| 3:15 PM – 3:20 PM | Transition from Continuous Trading Session (CTS) to CAS. Reference Price is calculated. No order placement or modification is permitted. |
| 3:20 PM – 3:25 PM | Order Entry Period. Fresh Market Orders and Limit Orders can be placed. Existing orders can be modified or cancelled within the applicable ±3% price band. |
| 3:25 PM – Random close between 3:28 PM and 3:30 PM | Only Limit Orders can be placed, modified, or cancelled. Market Orders cannot be modified or cancelled. |
| 3:30 PM – 3:35 PM | Auction matching takes place, trades are confirmed, and the equilibrium price becomes the official closing price. |
Frequently Asked Questions (FAQs)
What is the Closing Auction Session (CAS)?
The Closing Auction Session (CAS) is a new mechanism for determining the official closing price of eligible Cash Market securities. Instead of continuous trading determining the closing price, eligible buy and sell orders are matched during an auction, and a single equilibrium price becomes the official closing price.
When will the Closing Auction Session be implemented?
The Closing Auction Session (CAS) will be implemented effective August 3, 2026, as per SEBI and Exchange guidelines.
Which securities are covered under CAS?
CAS is applicable only to Cash Market securities in which derivative contracts are available.
Cash Market securities that are not eligible for CAS will continue to trade under the existing market timings until 3:30 PM.
How is the Reference Price calculated?
The Reference Price for CAS is calculated based on the Volume Weighted Average Price (VWAP) of trades executed between 3:00 PM and 3:15 PM.
Can I place orders during the Closing Auction Session?
Yes. During the Order Entry Period (3:20 PM to 3:25 PM), fresh Market Orders and Limit Orders can be placed.
From 3:25 PM until a random close between 3:28 PM and 3:30 PM, only Limit Orders can be placed, modified, or cancelled.
Are Stop Loss Orders and Iceberg Orders allowed during CAS?
No. Stop Loss Orders and Iceberg Orders are not permitted during the Closing Auction Session.
What is the applicable price band during CAS?
Trading during CAS is restricted to ±3% of the Reference Price.
What happens to pending orders from the Continuous Trading Session (CTS)?
Unexecuted Limit Orders from CTS will be carried forward to CAS, except Stop Loss Orders, Iceberg Orders, and orders outside the applicable CAS price band.
Are there any changes to Auto Square-off timings?
Yes.
For the Cash Market:
- Pre Auto Square-off will move from 3:15 PM to 3:05 PM.
- Auto Square-off will move from 3:20 PM to 3:10 PM.
For Equity Derivatives:
- Pre Auto Square-off remains 3:15 PM.
- Auto Square-off remains 3:20 PM.
Are there any changes to Equity Derivatives market timings?
Yes. Equity Derivatives market timings will be extended from 3:30 PM to 3:40 PM.
This extension is applicable to both Stock Derivatives and Index Derivatives.
